In a electrophotography or a electrostatic recording, there is formed an electrostatic latent image on a photo-conductor by a charging and a exposure process, and the latent image is developed by a developer and transferred to media, thereby being visualized as an image through a fusing process. Here, whether a clear image with excellent quality can be generated depends on various conditions in a developing and a fusing process. In a developing process, the quality of developed image is determined by electrical characteristics and a particle size of toner adhered to a latent image, and a degree of dispersion of various additives in a toner composition. In a fusing process, the image quality is determined by melt characteristics of toner fused and a degree of release property. Accordingly, the improvement of toner performance is required continuously.
There are a polymerization and a crushing method in methods of making toner. In the crushing method, there are mixed a binder resin, a colorant, charge control agents and release agents in a kneader, and, then, the mixture is heated, melted and crushed, thereby producing a toner. However, in the crushing method, it is impossible to disperse finely particles and, therefore, the additives are not able to function properly. Moreover, the yield of product having a desirable particle size is low because a range of particle distribution is broad, and toner performance tends to be poor because spherical particles are not produced.
There are emulsion aggregation and suspension polymerization steps in the polymerization method. The emulsion aggregation method comprises making latex through a emulsion polymerization of polymerizable monomer; mixing it with a colorant, charge control agents, release agents and so on; and heating them over several hours to tens hours with continuous agitation so that emulsion particles are aggregated, thereby forming desirable particles with a particular size. Examples of such method are disclosed in Japanese Patent Publication Nos. 63-282752, 63-282756 and 06-250439, U.S. Pat. Nos. 5,352,521, 4,996,127 and 4,797,339, Korean Patent Publication Nos. 1997-066730 and 1998-073192, and Korean Patent No. 0340303. However, the emulsion aggregation has a broad range of particle distribution and cannot produce fine particles because it is carried out through a long-running aggregation process. Another problem is poor fusing property due to a large molecular weight and high fusing point elasticity.
The suspension polymerization comprises pre-mixing monomers with a colorant, charge control agents and release agents; dispersing them using high shear force to form monomer drops, which can provide desirable particle diameters; adding a stabilizer and polymerizing them; and precipitating formed polymers to obtain polymer particles. An advantage of the suspension polymerization is to be able to produce fine particles of toner. Examples of such method are disclosed in Japanese Patent Publication Nos. 61-118758, 07-128909, and 09-311503, U.S. Pat. Nos. 5,219,697 and 5,288,577, Korean Patent Publication No. 2000-057424, and Korean Patent Nos. 0341786 and 0285183. However, the conventional suspension polymerization method has several problems. For one thing, it is difficult to adjust degree of polymerization because additives counteract polymerization reaction. Moreover, defectives can be produced by abnormal reactions due to instability. Another disadvantage is a poor fusing property due to a high softening point of the produced toner particles.